MORPHOLOGY AND PHYSIOLOGY 



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zoan may possess pseudopodia at one phase and flagella at an- 

 other phase during its life-cycle. Among numerous examples, 

 Naegleria (Fig. 79) and Trimastigamoeba (Fig. 79) may be 

 mentioned. Furthermore, pseudopodia and flagella may occur 

 at the same time, as in Dimorpha (Fig. 44), Actinomonas and 

 Ciliophrys (Fig. 44). In other cases such as Monomastix 

 (Fig. 147), a flagellum and cilia are present at the same time. 



Fig. 11 Diagrams showing possible development of a suctorian tentacle 

 from a cytostome and cytopharynx of a ciliate. (After Collin). 



Various types of cell-organs are present in the cytoplasm. 

 In Mastigophora, Ciliata and the majority of Sporozoa which 

 possess a definite body form due to the presence of a pellicle, 

 there occur in the cytoplasm highly contractile filaments known 

 as myonemes. In large forms they are noted in life, while in 

 smaller forms staining is required to show their presence. In the 

 hypermastigid Trichonympha, Kofoid and Swezy observed 

 longitudinal and transverse myonemes (Fig. 12). In the Ciliata 

 they are usually arranged parallel to the rows of cilia. In Stentor, 

 which is highly contractile, Schroder found that the myonemes 

 are lodged in canals located just below the alveolar layer. Each 

 myoneme is band-form and is said to be composed of alternating 

 light and dark parts. In some Sporozoa such as the gregarines, 

 the myonemes take chiefly a transverse course, and in the para- 

 sitic Mastigophora such as Trypanosoma, they are usually 

 parallel to the undulating membrane. 



In numerous ciliates, there occur characteristic structures 



